This subproject is one of many research subprojects utilizing the resources provided by a Center grant funded by NIH/NCRR. Primary support for the subproject and the subproject's principal investigator may have been provided by other sources, including other NIH sources. The Total Cost listed for the subproject likely represents the estimated amount of Center infrastructure utilized by the subproject, not direct funding provided by the NCRR grant to the subproject or subproject staff. Riboswitches are structured RNAs that controls gene expression at either transcription or translation level by changing their conformation upon binding of specific small molecules. In collaboration with Dr. Tina Henkins at Ohio State University, we have published crystal structures of two types of riboswitches that selectively binds to S-adenosyl methionine (SAM). These structures provided valuable insights into the ligand-recognition mechanism in these riboswitches. We seek to use APS beam time to determine the structure of SAM riboswitches in their apo forms, and bound to different SAM analogs.